Peanut plant growth was altered by monocropping-associated microbial enrichment of rhizosphere microbiome

Background and aims Repeated planting of the same or closely-related crop species often results in negative soil feedbacks, manifested as reduced plant growth. This is commonly attributed to accumulation of plant pathogenic organisms, but there is increasing evidence that other microbes may contribute as well. Since individual members of the bacterial soil microbiome display distinct preferences for specific root exudates, we hypothesize that enrichment of a small subset of bacterial species in the rhizosphere by monocropping will decrease overall diversity and thus negatively influence the performance of the crop. Methods To test this, we examined soil feedbacks for peanut plants inoculated with bacterial suspensions obtained from monocropped and rotated plots in closed cultivation systems. Results Partial 16S rRNA gene amplicon sequence analysis revealed significant effects of cropping system on the bacterial composition of peanut rhizospheres. When added to peanut seedling rhizospheres, soil suspensions derived from monocropped plots produced a significant reduction in rhizosphere microbiome species richness (number of OTUs). And, bacterial species including Sphingomonas sp., Herbaspirillum sp., and Arthrobacter sp. were enriched in peanut rhizosphere. However, monocropping-derived soil suspension inoculants showed significant deleterious effects on peanut development compared to rotation-derived inoculants. Further bioassays determined that some enriched bacterial strains that were isolated from the monocropping treatment repressed peanut hypocotyl extension. Conclusions Our results suggest that bacterial composition assembly in peanut rhizosphere in monocropping system especially that enriches particular deleterious bacterial taxa could lead to clear reductions in plant performance even in the absence of disease or signs of pathogenesis.